The invention relates to a nut system which is self-jamming at the time of tightening. A problem arises when a nut screwed onto a threaded rod clamps an easily deformable or fragile part. In such a case, a torque wrench which exerts only a strictly limited effort on the surface of the part is generally used. But in the case of accidental dismantling, a special wrench is not always available for re-assembly and in any case, such wrenches are expensive tools. The aim of the present invention is to overcome these drawbacks and to produce a nut system comprising a nut lock capable of locking the latter at any level of the threaded rod without requiring the use of special tools such as a torque wrench.
Self-locking nut systems of various kinds are known in the art as, for example, the system shown in British Pat. No. 520,537 of Apr. 26, 1940. However, such known systems require use of special tools such as a torque wrench and thus do not eliminate the problems hereinabove set forth.
This invention has among its objects a nut system which is self-blocking or jamming at the required time of tightening which eliminates the foregoing problems and which is composed of a nut and a nut lock element constituted by a non-threaded washer, characterized in that the nut and the washer are tied together while being rotatable relative to each other on a surface of revolution, the washer being situated adjacent the face of the nut pointing in the direction of the tightening and wherein the axes of the bores of the nut and of the washer are not coaxial with the axis of the surface of revolution.
In this way, at the beginning of the screwing of the nut onto a threaded rod, the nut and the washer whose axes and bores coincide will rotate together. When the washer comes into contact with the surface on which the nut is to be clamped, the friction of the washer on that surface prevents it from rotating while the nut continues to rotate. Thus, the two parts rotate relative to each other about the axis of the surface of revolution. The two axes of the bores of nut and washer cease to coincide and thus the washer is clamped or jammed securely against the screw, thus causing the locking or jamming of the system.
According to an embodiment of the invention which constitutes advantageous features, the said surface of revolution is generally conical widening in the direction of the tightening. The washer is thus joined rotatably at that surface.
To make the unscrewing of the system easier, it is preferable to increase the friction between the washer and the nut at their engagement at their coinciding surfaces of revolution in order to promote the concurrent driving of the washer by the nut during screwing onto the threaded rod at which time the axes of their bores coincide. For that purpose, it is possible, for example, to insert an elastic part between the neighboring or juxtaposed faces of the nut and of the washer, which part presses the coinciding surfaces of revolution of the washer and of the nut against each other. This elastic part may assume various forms. It may be in the form of a wire spring made of an elastic material or of a cambered ring of the type known as a "Belleville" ring. It may also be made of an elastomer, for example, in the form of a torus. In such case, the washer will preferably be made of a plastic material.